bridge: ebtables: fix reception of frames DNAT-ed to bridge device/port

When trying to redirect bridged frames to the bridge device itself or
a bridge port (brouting) via the dnat target then this currently fails:

The ethernet destination of the frame is dnat'ed to the MAC address of
the bridge device or port just fine. However, the IP code drops it in
the beginning of ip_input.c/ip_rcv() as the dnat target left
the skb->pkt_type as PACKET_OTHERHOST.

Fixing this by resetting skb->pkt_type to an appropriate type after
dnat'ing.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>